With the interest in 43 foot untuned verticals, and some of the less than accurate claims being made, I thought I’d share the results of a 25 foot untuned vertical antenna I developed a few years ago. Hopefully, I can shed some more light on its practical use, as well as show how to gain a bit more performance.

During recent range testing of a hexbeam I needed a horizontally-polarised resonant antenna covering 20m thru 10m which could be assembled and disassembled quickly and easily. The cobweb antenna meets the requirement nicely – it comprises 5 parallel dipoles bent into a square shape and mounted on a support structure made of fibreglass poles.Continue reading Classic Amateur Radio (G3TXQ) – Cobweb Antenna

Few antennas polarise opinion as much as the G5RV – it seems you either swear by it or swear at it! The purpose of this article is to present a few technical facts about the antenna and allow the reader to judge whether or not it might be useful for them.

1. Arrival angles

In “Hexbeam Height (Part 1)” we looked at how a Hexbeam’s height above ground affected its directivity and its tuning. We came to the conclusion that “higher is better” when the objective is to maximise the antenna’s performance at very low take-off angles. However, depending on our operating interests this may not be an appropriate criteria; so in this section we will look in more detail at signal arrival-angles for different HF bands and paths, and how they play against the Hexbeam’s height.

A question often asked on the Yahoo HexBeam discussion group is “what is the best height for my Hexbeam?”. It is difficult to answer the question without first understanding what the questioner means by “best”. As with any antenna, height above ground affects the tuning of the Hexbeam, its directivity and its matching; so the height which produces the lowest SWR might well be different from the height which produces best F/B or acceptable Gain.

To illustrate how a Hexbeam’s performance varies with height, a 20m Classic monobander was modelled at 5ft intervals between 10ft and 60ft over Real/Average ground [Results would have followed the same trends had a Broadband Hexbeam been modelled]. The following charts show the results. Assuming that most readers will be interested in the performance of the antenna over long distance paths, the Gain and F/B figures were modelled at a 5° take-off angle. The charts can be used to predict performance on other bands by scaling the height axis accordingly; for example on 10m the height axis would run from 5ft to 30ft.

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“I measured 3 turns of RG58, solenoid wound with a 1.5” internal diameter, to be self resonant in the 2m band. Anything radically different in number of turns or diameter had mediocre choking impedance.